Crystal structure of methyl β-D-hamameloside

The crystal structure of methyl -D-hamameloside has been determined by direct methods. The trigonal crystals have the space groupR3. Referred to hexagonal axes, there are nine molecules in the non-primitive unit cell witha =b = 18·08(2),c = 7·22(2)Å. The molecule exists in the 1C-trans-chair conformation, with the mean C-C and C-O bond lengths being 1·531 and 1·428Å respectively. The mean value for the carbon bond angle is 110·2 °. The crystal structure is composed of columns of molecules hydrogen-bonded about 3₂ axes, and with van der Waals forces holding these columns together around the 3₁ and 3-fold axes.     

Excess enthalpies and apparent molar volumes of some N-methyl substituted amino acids in aqueous solutions

The excess enthalpies and limiting partial molar volumes at 25°C for aqueous solutions of N-methyl glycine, N-methyl alanine, and N-methyl serine are reported and compared with the same properties for the parent amino acids. For each N-methyl derivative the enthalpic contribution to the pairwise interaction is less favorable than that for the parent amino acid. The contribution of the N-methyl substituent to V ₂ ⁰ is similar for each amino acid, and is about 2 cm³-mol^–1 greater than for a methyl substituent on the -carbon. These observations have been rationalized in terms of the likely solute-solvent interactions. In addition a rigid particle model is used with the volume data to examine solute-solvent interactions.     

Electrochemical detection of nanoscale phase separation in binary self-assembled monolayers

Developing methods to probe the nature and structure of nanoscale environments continues to be a challenge in nanoscience. We report a cyclic voltammetry investigation of the internal, hydrogen-bond-driven phase separation of amide-containing thiols and alkanethiols. Amide-containing thiols with a terminal ferrocene carboxylate functional group were investigated in two binary monolayers, one homogeneously mixed and the other phase separated. The electrochemical response of the ferrocene probe was used to monitor adsorbate coverage, environment, and phase separation within each of these monolayers. The results demonstrate that the behavior of ferrocene-containing monolayers can be used to probe nanoscale organization.     

Specific ethene surface activation on silver oxide covered Ag[111] from the interplay of STM experiment and theory

High-resolution scanning tunneling microscopy (STM) images at 5 K, simultaneously resolving the molecular adsorbate and the honeycomb structure of the well-defined Ag[111]-p(4 x 4)+Ag(1.83)O substrate, assign the adsorption site for ethene on the silver oxide surface. Ethene molecules are exclusively adsorbed above a particular subset of Ag(delta)(+) sites in the hexagonal rings of the oxide. Extensive density functional theory (DFT) slab calculations confirm that this is the most stable site, with an adsorption energy of 0.4 eV (39 kJ mol(-1)). Adsorption is accompanied by a large deformation of the hexagonal oxide ring and a significant increase in the C-C bond length. STM image simulations provide qualitative agreement with the experimental images, and the molecular orientation is discussed with the help of simple molecular orbital arguments.     

Peroxycarbenium-mediated C-C bond formation: applications to the synthesis of hydroperoxides and peroxides

The Lewis acid-mediated reaction of alkene nucleophiles with peroxyacetals provides an effective route for the synthesis of homologated peroxides and hydroperoxides. In the presence of Lewis acids such as TiCl(4), SnCl(4), and trimethylsilyl triflate, peroxyacetals and peroxyketals undergo reaction with allyltrimethylsilane, silyl enol ethers, and silyl ketene acetals to afford homoallyl peroxides, 3-peroxyketones, and 3-peroxyalkanoates, respectively. Reactions of peroxyacetals are Lewis acid dependent; TiCl(4) promotes formation of ethers while SnCl(4) and trimethylsilyl triflate promote formation of peroxides. Lewis acid-promoted reactions of silylated hydroperoxyacetals furnish silylated hydroperoxides, which can be deprotected to homologated hydroperoxides. Hydroperoxyketals undergo Lewis acid-mediated allylation to furnish 1,2-dioxolanes via attack of hydroperoxide on the intermediate carbocation. Lewis acid-mediated cyclization of unsaturated peroxyacetals furnishes 1,2-dioxanes, 1,2-dioxepanes, and 1,2-dioxacanes through 6-endo/exo, 7-endo/endo, and 8-endo/endo pathways. The corresponding reactions involving 6-endo/endo and 5-endo/exo pathways were unsuccessful.